System and method for determining ground stiffness

ABSTRACT

A compactor is disclosed that has at least one roller drum configured to compact a work material. The compactor also has a memory storing a calibration system. The calibration system has a plurality of reference propelling power values, a plurality of reference ground stiffness values, and correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values. The compactor further has a processor. The processor is configured to determine a propelling power of the compactor. The processor is also configured to compare the propelling power of the compactor with at least one of a plurality of reference propelling power values in the calibration system. The processor is further configured to determine a stiffness value of the work material based on a relationship between the propelling power of the compactor and the at least one of the plurality of reference propelling power values.

TECHNICAL FIELD

This disclosure relates generally to machines that compact material, and more particularly, to a system and method for determining ground stiffness during a ground compaction process.

BACKGROUND

Compacting machines or compactors are commonly used to compact work materials (such as soil, gravel, asphalt) to a desired density while constructing buildings, highways, parking lots, and other structures. Often, earthen material at a worksite must be compacted and one or more compacting machines must be involved to successively compact material until the desired level of compaction is achieved. The process may require many passes over the work material to reach the desired level. Stiffness is one measurement used to determine the level of compaction.

There are a variety of methods for determining the stiffness of a soil or other material. Current technology includes the use of nuclear density gauges, plate load test devices, falling weight deflectometers, or the like, which measure soil density or soil stiffness either before and/or after a compaction process. Although this may provide an accurate measurement for the compaction of the soil or other material, these measures must be performed separately from the compaction process. Systems for measuring compaction during the compaction process are known. For example, U.S. Pat. No. 8,057,124 B2 (the “'124 patent”), assigned to Wacker Neuson Produktion GmbH & Co., discloses a method and device for measuring soil parameters. It uses an approximation of the actual gradient of the contact force and a contact surface parameter to calculate a dynamic modulus of deformation. However, this modulus is dimensionless. In addition, the method disclosed by the '124 patent is limited to vibratory compacting machines because the analysis used in the method requires measurement of the contact force and contact distance of a vibrated contact element.

Current methods fail to provide a measure of stiffness with an engineering unit that can be determined during the compaction process performed by a non-vibratory, static compacting machine. While a unitless stiffness indicator for such a machine is available, the unitless stiffness indicator cannot be used for other purposes, such as by a design engineer who needs to know the specific compaction of the soil or other material in order to build or design roads, building pads, etc. Another disadvantage is that the unitless stiffness indicator is often machine dependent, and therefore difficult to be utilized across multiple machines. The present disclosure is directed to overcoming or mitigating one or more of these problems set forth.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to a compactor. The compactor includes at least one roller drum configured to compact a work material. The compactor also includes a controller. The controller is configured to determine a propelling power of the compactor. The controller is further configured to access a calibration system including a reference propelling power value and correlation information between the reference propelling power value and a reference ground stiffness value. The controller is further configured to compare the propelling power of the compactor with the reference propelling power value. The stiffness value of the work material is determined based on a relationship between the propelling power of the compactor and the reference propelling power value. In addition, the compactor is configured to adjust a compaction effort based on the determined stiffness value.

In another aspect, the present disclosure is directed to a compactor. The compactor includes at least one roller drum configured to compact a work material. The compactor also includes a memory storing a calibration system. The calibration system includes a plurality of reference propelling power values, a plurality of reference ground stiffness values, and correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values. The compactor further includes a processor. The processor is configured to determine a propelling power of the compactor. The processor is further configured to compare the propelling power of the compactor with at least one of the plurality of reference propelling power values in the calibration system. In addition, the processor is configured to determine a stiffness value of the work material based on a relationship between the propelling power of the compactor and the at least one of the plurality of reference propelling power values.

In a further aspect, the present disclosure is directed to a system for compacting at least one work material on a work site. The system includes a compactor having a variable compaction effort setting mechanism. The system also includes a memory storing a calibration system. The calibration system includes a plurality of reference propelling power values, a plurality of reference ground stiffness values, and correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values. The system further includes a processor. The processor is configured to determine a propelling power of the compactor. The processor is further configured to compare the propelling power of the compactor with at least one of the plurality of reference propelling power values in the calibration system. In addition, the processor is configured to determine a stiffness value of the work material based on a relationship between the propelling power of the compactor and the at least one of the plurality of reference propelling power values. Moreover, the processor is configured to produce a ground stiffness map for the work site based on the determined stiffness value and location information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary embodiment of a compactor;

FIG. 2 is a block diagram of an exemplary embodiment of a controller;

FIG. 3 is a diagrammatic illustration of an exemplary roller drum on a portion of work material to be compacted; and

FIG. 4 is a flow chart illustrating an exemplary method of determining a stiffness value of a work material.

DETAILED DESCRIPTION

FIG. 1 is a diagrammatic illustration of an exemplary compactor, according to one aspect of the disclosure. In FIG. 1, an exemplary compactor 10 is shown that can travel over a surface 16 and compact a work material 14 under its own power. Work material 14 may include soil, gravel, asphalt, etc. Types of compactors contemplated to implement the disclosed process and device include soil compactors, asphalt compactors, utility compactors, pneumatic compactors, vibratory compactors, self-propelled two-wheel and four-wheel compactors, and tow-behind systems. Compactor 10 includes a body or frame 12 that inter-operatively connects and associates the various physical and structural features that enable compactor 10 to function. These features may include an operator cab 20 that is mounted on top of frame 12 from which an operator may control and direct operation of compactor 10. Additionally, a steering feature 21 and similar controls may be located within operator cab 20. To propel compactor 10 over surface 16, a power system (not shown), such as an internal combustion engine, can also be mounted to frame 12 and can generate propelling power to physically move compactor 10. One or more other implements (not shown) may be connected to compactor 10. Such implements may be utilized for a variety of tasks, including, for example, loading, lifting, and brushing. Such implements may include, for example, buckets, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others.

To enable physical motion of compactor 10, the illustrated compactor 10 includes a first roller drum 24 and a second roller drum 22 that are in rolling contact with surface 16. It should be appreciated that compactor 10 may have a single roller drum and rubber tires for compacting work material 14, and the roller drums (or roller drum in the case of a single-drum compactor) may be smooth or equipped with compacting feet, such as a padfoot type design or a tamping foot type design. For reference purposes, compactor 10 can have a typical direction of travel such that roller drum 24 may be considered the front drum and roller drum 22 considered the rear drum of compactor 10. Front drum 24 and rear drum 22 can be cylindrical structures that are rotatably coupled to and can rotate with respect to frame 12. Because of their front and rear positions and their dimensions, front drum 24 and rear drum 22 support frame 12 of compactor 10 above surface 16 and allow compactor 10 to travel over surface 16. Front drum 24 and rear drum 22 are oriented generally transverse or perpendicular to the direction of travel of compactor 10. It should be appreciated that because compactor 10 is steerable, the forward direction of travel may change bearing during the course of operation but can be typically assessed by reference to the direction of movement of front drum 24. In the illustrated embodiment, to transfer motive power from the power system to surface 16, the power system can operatively engage and rotate rear drum 22 through an appropriate power train.

In some embodiments, compactor 10 may have a variable compaction effort setting mechanism, such as variable vibratory mechanism 25. Variable vibratory mechanism 25 may be disposed inside the interior volume of roller drum 24 and/or 22. According to one exemplary embodiment, variable vibratory mechanism 25 includes one or more weights or masses disposed inside the roller drum at a position off-center from the axis line around which the roller drum rotates. For example, FIG. 1 shows two weights disposed inside roller drum 24 (and similarly roller drum 22). As the roller drum rotates, the off-center or eccentric positions of the weights induce oscillatory or vibrational forces to the roller drum that are imparted to the surface being compacted. The weights are eccentrically positioned with respect to the common axis and are typically movable with respect to each other about the common axis to produce varying degrees of imbalance during rotation of the weights. The amplitude of the vibrations produced by such an arrangement of eccentric rotating weights may be varied by positioning the eccentric weights with respect to each other about their common axis to vary the average distribution of mass (i.e., the centroid) with respect to the axis of rotation of the weights. For example, referring the FIG. 1, the two weights inside roller drum 22 are positioned closer to each other than the two weights insider roller drum 24. As a result, the centroid of the two weights inside roller drum 22 may be at a position farther away from the common axis than that of the two weights inside roller drum 24. Vibration amplitude in such a system increases as the centroid moves away from the axis of rotation of the weights and decreases toward zero as the centroid moves toward the axis of rotation. Varying the rotational speed of the weights about their common axis may change both the amplitude and the frequency of the vibrations produced by such an arrangement of rotating eccentric weights. In some embodiments, the eccentrically positioned masses are arranged to rotate inside the roller drum independently of the rotation of the roller drum. In some embodiments, the compaction effort (e.g., the amplitude and/or frequency of the vibratory force) may be varied depending on the stiffness of the material being compacted. The present disclosure is not limited to these embodiments described above. According to other alternative embodiments, any variable vibratory mechanism 25 that modifies the compaction effort of the first roller drum 24 or the second roller drum 22 may be used.

Variable vibratory mechanism 25 controls the compaction effort for first and second roller drums 24, 22. By altering the distance of the eccentric weights from the axis of rotation in variable vibratory mechanism 25, the amplitude portion of the compaction effort is modified. By altering the speed of the eccentric weights around the axis of rotation in variable vibratory mechanism 25, the amplitude and frequency portions of the compaction effort are modified. Additionally, both the amplitude portion and the frequency portion of the compaction effort of variable vibratory mechanism 25 can be modified by changing both the distance of the eccentric weights from the axis of rotation and the speed of rotation of the eccentric weights around the axis of rotation at the same time.

To facilitate control and coordination of compactor 10, compactor 10 may include a controller 40 such as an electronic control unit. While controller 40 illustrated in FIG. 1 is represented as a single unit, in other aspects controller 40 may be distributed as a plurality of distinct but interoperating units, incorporated into another component, or located at a different location on or off compactor 10. FIG. 2 illustrates a block diagram of an embodiment of controller 40 comprising exemplary components. Controller 40 may include a sensor 32, an input device 39, a processor 42, a memory 44, a location sensor 46, and a display or output 48. The main unit of controller 40 may be located in operator cab 20 for access by the operator and may communicate with steering feature 21, the power system, and with various other sensors and controls on compactor 10.

Sensor 32 may be configured to sense one or more parameters indicative of the acceleration, speed, torque, power, force, or other operating features of compactor 10 or one or more components of compactor 10. The components may include front drum 24, rear drum 22, frame 12, or the like. Sensor 32 may include a signal transducer configured to sense a transmitted signal, or component of a transmitted signal. The transmitted signal may include an electric signal, an RF signal, a sonic signal, an optical signal such as a laser signal, or other types of signals. As used herein, sensor 32 is used as a reference to encompass multiple sensors that may be used by or located on compactor 10. These sensors may or may not be physically located together, and may serve different functions. For example, sensor 32 may include a ground speed sensor to sense the ground speed of compactor 10. In another example, sensor 32 may include an inclinometer to sense the slope of surface 16.

Location sensor 46 may be configured to receive location information, such as global or local positioning data used in establishing and tracking geographic position of compactor 10 within a work area. For example, location sensor 46 may include a GPS system, a laser plane system, a dead reckoning system, or the like.

As illustrated in FIG. 2, processor 42 may be coupled to sensor 32 and location sensor 46. Processor 42 may be configured to output signals that are responsive to inputs from sensor 32, as further described herein. A display 48 may also be coupled with the processor 42 and may be positioned in operator cab 20 to display various data to an operator relating to the machine position, ground speed, ground stiffness, or other parameters. Action may be taken in response to the ground stiffness or other compaction metrics, including commencing the compaction process within the work area, stopping travel of compactor 10, or redirecting or otherwise changing a planned compactor travel path or coverage pattern.

Processor 42 utilizes the values sensed by sensor 32 that may be stored in computer readable memory 44 to determine a stiffness value of working material 14 using algorithms and/or data stored in memory 44. Processor 42 may compare the determined stiffness value to a predetermined threshold, such as a minimum stiffness value that may have been input by input device 39. If the determined stiffness value meets or exceeds the minimum stiffness value, processor 42 may send a signal to display 48 communicating that work material 14 has been sufficiently compacted. If the stiffness value does not meet or exceed the minimum stiffness value, then processor 42 may send a signal to display 48 communicating that further compaction is required. Examples of processors include computing devices and/or dedicated hardware as defined herein, but not limited to, one or more central processing units and microprocessors.

The computer readable memory 44 may include random access memory (RAM) and/or read-only memory (ROM). Memory 44 may store computer executable code including a control algorithm for determining a stiffness value of work material 14 responsive to inputs from sensor 32. Memory 44 may also store various digital files including the values sensed by sensor 32 or location sensor 46. Memory 44 may also store a calibration system (e.g., a database, an algorithm, a lookup table, etc.) including information for determining a stiffness value of work material 14. Memory 44 may also store information input from input device 39. The information stored in memory 44 may be provided to processor 42 so that processor 42 may determine a stiffness value.

Display 48 may be located either on compactor 10, located remotely, or may include multiple displays both on compactor 10 and remotely, and may include, but not limited to, cathode ray tubes (CRT), light-emitting diode display (LED), liquid crystal display (LCD), organic light-emitting diode display (OLED) or a plasma display panel (PDP). Such displays can also be a touchscreen. Input device 39 may include a keyboard, a mouse device, a touch screen, one or more control features (e.g., buttons, control sticks, dials, etc.), or other suitable devices for inputting information.

FIG. 2 also shows a torque converter or hydraulic drive motor 52. Torque converter or hydraulic drive motor 52 may be used to determine a propelling power of compactor 10. When a torque converter is used (e.g., when compactor 10 is a static compactor), torque converter 52 may be located in the power train of compactor 10 for transferring rotating power from the engine of compactor 10 to a rotating driven load, such as rear drum 22. In some embodiments, an input sensor 54 and an output sensor 56 may be located at the input and output of torque converter 52, respectively. Sensor 54/56 may be used to sense the speed (e.g., in RPM) at the input/output of torque converter 52. The speed signals sensed by sensors 54 and 56 may be used by processor 42 to determine a differential speed or to calculate the torque at the output of torque converter 52. In some embodiments, output sensor 56 may measure the output torque directly and input sensor 54 may be omitted. When a hydraulic drive motor is used (e.g., when compactor 10 is a vibratory compactor), sensors 54/56 may be used to sense the pressure at the input/output of hydraulic drive motor 52. The pressure signals sensed by sensors 54 and 56 may be used by processor 42 to determine a differential pressure or to calculate a drive torque at hydraulic drive motor 52. In some embodiments, output sensor 56 may measure the drive torque directly and input sensor 54 may be omitted.

FIG. 3 is a diagrammatic illustration of a cross-section of a volume of work material 14 being compacted by a roller drum (e.g., forward drum 24 or rearward drum 22) having a width W. Work material 14 has a thickness T, which may decrease during the compaction process.

FIG. 4 is a flowchart depicting a method for determining a stiffness value of work material 14 undergoing compaction using compactor 10, according to an embodiment of this disclosure. During the compaction process, processor 42 may be configured to determine the real-time or near real-time propelling power of compactor 10. Using the propelling power and a calibration system, processor 42 can determine a real-time or near real-time stiffness value of work material 14.

In step 110, processor 42 determines a ground speed of compactor 10. As described above, sensor 32 may include a ground speed sensor for sensing the ground speed of compactor 10. Processor 42 reads information from the ground speed sensor to determine the ground speed of compactor 10.

In step 120, processor 42 determines a rolling resistance of compactor 10. For example, when a torque converter is used, processor 42 may determine the rolling resistance based on a differential speed, an output torque of torque converter 52, or a combination of these parameters. As described above, sensors 54 and 56 may be used to sense the differential speed and sensor 56 may be used to sense the output torque. In another example, compactor 10 may include a hydraulic drive motor in the power system (e.g., when 52 is a hydraulic drive motor) and the rolling resistance may be determined based on measuring of the drive torque. The drive torque, in turn, can be measured based on a differential pressure from the hydraulic drive motor. As described above, sensors 54 and 56 may be used to sense the differential pressure and sensor 56 may be used to sense the drive torque. The output/drive torque of compactor 10 can also be measured by other methods such as instrumented drive shafts or axles. In some embodiments, processor 42 may also determine a slope resistance of compactor 10 and use the slope resistance to compensate for the rolling resistance. For example, the rolling resistance may be increased or decreased based on the slope resistance. As described above, sensor 32 may include an inclinometer to sense the slope of surface 16. The slope resistance may be determined by processor 42 by reading information from the inclinometer. Alternatively, other types of slope measuring devices, e.g., GPS antennas (e.g., as part of location sensor 46), laser plane detectors, and the like, can be used in the determination of the slope resistance. In some embodiments, if a geographical model of the work site is known, the slope of surface 16 may be determined based on information from the geographical model for a given moving direction of compactor 10. As the compacting operation proceeds, the geographical model may be updated to account for the geographical changes caused by the compacting operation.

In step 130, processor 42 determines a propelling power of compactor 10. In one embodiment, the propelling power is determined based on the ground speed and the rolling resistance. For example, the propelling power (PP) is determined as the product of the ground speed (GS) and the rolling resistance (RR): PP=GS×RR. In another example, the propelling power is determined as the product of the output torque (OT) and the output speed (e.g., rotational velocity) (OS) of torque converter 52: PP=OT×OS. In another example, the propelling power is determined as the product of the differential pressure (DP) and a hydraulic flow rate (FR): PP=DP×FR. In other embodiments, the propelling power can be determined by other methods. For example, the propelling power can be determined based on the rate of fuel consumption.

The propelling power may correspond to a compactive energy delivered by compactor 10 to work material 14. Therefore, the propelling power may also be determined based on a determination of the compactive energy. Determination of the compactive energy may require knowledge of certain characteristics of work material 14, such as the lift thickness T. The lift thickness T may be determined based on measuring an elevation of work material 14 using, for example, a laser plane system, a GPS system, manual survey techniques, etc. Determination of the compactive energy may also require knowledge of the compaction width CW. The compaction width CW may be known in advance. For example, in some embodiments the compaction width CW is the same as or about the width of the roller drum W used for the compaction operation. In other embodiments, the compaction width CW may not be the same as or about the width of an individual roller drum. For example, the forward drum 24 may have a different width from the width of rearward drum 22. In these embodiments, the compaction width CW is the effective width of compaction by compactor 10.

Once the lift thickness T and the compaction width CW are determined or known, processor 42 may determine the compactive energy (CE) (also known as the specific compactive energy) delivered from compactor 10 to work material 14 based on T, CW, and the rolling resistance RR. For example, compactive energy CE can be determined as CE=RR/(T×CW). The determined compactive energy may be used to further determine the propelling power PP based on the correlation between CE and PP.

In some embodiments, the propelling power may be further compensated by taking into account factors including the rate of energy loss internal to compactor 10 (PP_(int)), such as losses in bearings, gears, torque converters, hydraulic fluid, etc.; the rate of gain of potential energy of compactor 10 (PP_(pot)), and the rate of wind energy being applied to compactor 10 (PP_(wind)). The rate of gain of potential energy of compactor 10 (PP_(pot)) may be determined based on the weight of compactor 10, the slope of surface 16, and the ground speed of compactor 10. The rate of wind energy applied to compactor 10 (PP_(wind)) may be determined as a function of the speed and the direction of the wind relative to the direction of compactor 10. The net propelling power PP_(net) (i.e., the propelling power after compensation) may be determined as PP_(net)=PP−PP_(int)−PP_(pot)−PP_(wind).

The propelling power may be related to ground stiffness. For example, stiffer and stronger ground surfaces require less power to move compactor 10 and vice versa. By comparing the propelling power with a predetermined power value, for example, a power value that indicates the ground stiffness satisfies compaction requirements, a relative measure can be obtained reflecting the progress of the compaction process. However, such relative measure is unitless and often machine dependent. To obtain a stiffness value having an engineering unit and/or be machine independent, the propelling power can be calibrated to convert the propelling power into a stiffness value having a unit of, for example, force per area. In some embodiments, the unit of force per area may be in the form of pounds per square inch (psi). The calibration process will be described below with respect to steps 140, 150, and 160.

In step 140, processor 42 may access a calibration system. The calibration system may include a database, a program, an algorithm, a lookup table, or other suitable information for calibrating the propelling power. The calibration system may be in the form of a software package, a hardware component, or a combination thereof. For example, the calibration system may be a software package that is stored in memory 44 and accessible by processor 42. In another example, the calibration system may be a hardware component located on compactor 10 and coupled to processor 42, which may access information stored in the hardware component.

The calibration system may include a plurality of reference propelling power values, a plurality of reference ground stiffness values, and correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values. For example, the calibration system may include a set of reference propelling power values relevant to compactor 10, which may include a minimum reference power value indicating the minimum propelling power required to drive compactor 10 over surface 16 of work material 14 that has been compacted to a sufficiently stiff state. Similarly, the set of reference propelling power values may include a maximum reference power value indicating the maximum propelling power of compactor 10. Intermediate reference power values may also be included.

The calibration system may also include a set of reference ground stiffness values. The set of reference ground stiffness values may include physical characteristic parameters of work material 14 being compacted, including a stiffness value with a unit of force per area or psi or Pascal (units of pressure), a modulus of resilience or Young's modulus (also in the units of pressure), or other parameters indicating the stiffness or strength of work material 14. The reference ground stiffness values may be compared directly with compaction acceptance or quality assurance requirements.

The calibration system may also include correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values. For example, a particular propelling power used to drive compactor 10 on surface 16 of a particular work material 14 may correspond to a particular ground stiffness of the particular work material 14. The calibration system may include information of a link between a particular reference propelling power value and a particular reference ground stiffness value. The correlation between such a reference propelling power value and a reference ground stiffness value may be established by field measurement and/or laboratory test. In case of field measurement, the reference ground stiffness value can be obtained by means of plate load testing or falling weight deflectometers. The field measurement may be conducted with respect to a particular compactor or a plurality of compactors having similar specifications. For example, compactor 10 may record the propelling power values (e.g., as determined in step 130) when performing a compacting task. During the compaction process, the ground stiffness of the work material being compacted can be measured. The measurement results can be associated with the recorded propelling power values for the particular work material. In the case of a laboratory test, a database including soil characteristics (e.g., soil type, soil density, the moisture content of soil, etc.) and machine performance characteristics (e.g., propelling power, compactive energy delivered from the machine to the work material, etc.) in response to the soil characteristics may be established. In addition to the soil characteristics, soil strength indicators such as stiffness values or modulus of resilience values may also be added to the database based on laboratory test or analysis. The stiffness values or modulus of resilience values may be obtained for different soil density and moisture content, and for different soil types. As a result, the calibration system may contain correlated propelling power values and ground stiffness values. In some embodiments, a propelling power value may correspond to different ground stiffness values for different soil types, soil densities, and moisture contents. Similarly, a ground stiffness value may correspond to different propelling power values for different soil types, soil densities, and moisture contents. The propelling power values and ground stiffness values in the calibration system are referred as reference propelling power values and reference ground stiffness values, respectively.

The reference propelling power values and reference ground stiffness values in the calibration system may be organized in various forms. For example, these values may form a lookup table with the propelling power values as indices. In another example, a function may be established to approximate the relationship between the reference propelling power values and the reference ground stiffness values. Curve fitting methods may be used to establish the function.

In step 150, processor 42 may compare the propelling power of compactor 10 determined in step 130 with one or more reference propelling values in the calibration system. For example, the propelling power of compactor 10 may be compared with a reference propelling value that is close to the propelling power.

In step 160, processor 42 may determine the stiffness value of work material 14 based on a relationship between the propelling power of compactor 10 and the reference propelling power value that is compared with in step 150. If the two values are the same, then processor 42 may determine that the stiffness value of work material 14 is equal to or substantially the same as the reference ground stiffness value corresponding to the reference propelling power value. If the two values are different, then processor 42 may take different approaches to determine the stiffness value of work material 14. In one embodiment, processor 42 may search for the closest reference propelling power value to the propelling power of compactor 10 in the calibration database and use the reference ground stiffness value corresponding to the closest reference propelling power value as the stiffness value of work material 14. In other embodiments, more accurate approaches may be used. For example, a difference between the propelling power of compactor 10 and a reference propelling power value may be computed. A compensation value may be determined based on the difference and added to the reference ground stiffness value corresponding to the reference propelling power value. The compensated reference propelling power value may be used as the stiffness value of work material 14. In another example, a regression method may be used in which a statistical model may be established based on the existing data in the calibration system. The statistical model may estimate an expectation of the stiffness value given the condition of a propelling power value (e.g., a conditional expectation). The statistical model may be trained using the plurality of reference propelling power values and reference ground stiffness values. The trained model may be used to determine the stiffness value of work material 14 based on the determined propelling power of compactor 10.

As described above, the reference ground stiffness values in the calibration system are physical characteristics parameters of the work material such as modulus of resilience values or Young's modulus values. These reference ground stiffness values may have a unit of pressure, such as force per area, psi, or Pascal. Therefore, the stiffness value of work material 14 may also have such units.

As described above, because a particular reference propelling power value may correspond to different reference ground stiffness values for different types, densities, and/or level of moisture contents of the work material, the correlation information (e.g., between a reference propelling power value and a reference ground stiffness value) used in the determination of the stiffness value may be different for work materials of different types, densities, and moisture contents. Therefore, these properties of the work material being compacted may be compared with the relevant reference material information in the calibration system to determine proper correlation information. Based on the comparison, processor 42 may determine the proper reference propelling power value and/or reference ground stiffness value for determining the stiffness value of the work material.

The determination of the stiffness value may be performed during the compaction process by processor 42. Once the stiffness value is determined, at step 170, processor 42 may compare the stiffness value to a predetermined threshold stiffness value for the work area being compacted. The threshold stiffness value may be a value input by a user via input device 39 or a stored value. At step 180, if the stiffness value is below the threshold, processor 42 may send a signal to display 48 to indicate that further compaction is required. The operator may compact work material 14 further by performing more passes until the determined stiffness value reaches the threshold stiffness value. The process steps 110, 120, 130, 140, 150, and 160 are then repeated for each continuing compactor pass. Once the stiffness value reaches the threshold stiffness value required for the work area, then processor 42 may send a signal to display 48 that no further compaction is needed and the process ends at 190.

In some embodiments, the stiffness value of work material 14 may be determined and displayed on display 48 in real-time or near real-time. In addition, display 48 may indicate the location of compactor 10 in real-time geographic coordinates. For example, the stiffness value may be displayed in color on a map of the work site to indicate the completed areas and areas needing more compaction passes. In another example, the stiffness information may be displayed in graphical, textual, tabular, numerical, or any other types of formats desired to effectively display the information.

In some embodiments, compactor 10 may be configured to adjust a compaction effort based on the determined stiffness value. For example, compactor 10 may use variable vibratory mechanism 25 to control the compaction effort, as described above. Depending on the determined stiffness value, the compaction effort may be adjusted to be higher or lower. For instance, if the determined stiffness value is lower than a desired stiffness value or a predetermined threshold, the compaction effort may be increased to achieve the desired stiffness value or the predetermined threshold. In another example, the compaction effort may be adjusted by taking additional compaction passes.

Some embodiments may involve a system for compacting at least one work material on a work site. The system may include one or more compactors having a variable compaction effort, such as compactor 10. The system may also include a memory for storing the calibration system and a processor for performing various tasks. The memory/processor may be provided on one or more compactors, or may be provided as part of a separate control unit. As described above, the processor may be configured to determine a stiffness value of the work material being compacted by a compactor of the system. The processor may also produce a ground stiffness map for the work site based on the determined stiffness value and location information. For example, the processor may associate the determined stiffness value with a geographic location on a map of the work site. The geographic location information may be obtained by location sensor 46. The produced ground stiffness map may be displayed on display 48.

The determined stiffness value may be compared with a desired stiffness value. The desired stiffness value may be provided to the processor or input by an operator of the system. The desired stiffness value may be related to a quality standard, such as the stiffness value to be achieved by the compaction operation. The processor may indicate on the ground stiffness map the progress of achieving the desired stiffness value. For example, the ground stiffness map may indicate the current ground stiffness of one or more locations on the work site compared to the desired stiffness value. In one embodiment, the ground stiffness map may use color maps to indicate areas having achieved the desired stiffness and/or areas needing more compaction. For areas needing more compaction, the ground stiffness map may use different colors or shadings to indicate how close between the current stiffness and the desired stiffness.

In some embodiments, the processor may command one or more compactors to adjust the compaction effort to achieve the desired stiffness value based on the determined stiffness value (e.g., the current stiffness) and/or the ground stiffness map. As described above, the compaction effort may be adjusted using variable vibratory mechanism 25 or by taking additional compaction passes. In some embodiments, the ground stiffness map may indicate the areas needing adjusted compaction effort and/or the degree of adjustment based on the difference between current stiffness and the desired stiffness.

In some embodiment, the processor may produce the ground stiffness map based on stiffness values determined from multiple compactors. For example, two or more compactors may operate on the work site to compact one or more work materials. Information obtain from multiple compactors may be processed to determine the ground stiffness map. For example, a first stiffness value of a first work material being compacted by a first compactor may be mapped to the ground stiffness map at a first location. Similarly, a second stiffness value of a same or different work material being compacted by a second compactor may be mapped to the ground stiffness map at a second location. In addition, the processor of the system may command multiple compactors to achieve the desired stiffness value. Using more than one compactor to operate on a work site may improve the speed of the compaction operation.

INDUSTRIAL APPLICABILITY

The present disclosure provides an advantageous system and method for determining the stiffness value of a work material during a compaction process. The system uses the operation parameters of the compactor in conjunction with a calibration system to accurately and efficiently determine a real-time or near real-time stiffness value having an engineering unit. Instead of requiring a multiple step process for compacting a work material and measuring the stiffness, this system synthesizes the compaction and determination of the stiffness into one process.

The system and method allow a compaction machine operator to obtain an accurate indication of the compaction response of one or more materials being compacted. Specifically, the operator may be able to accurately determine when the work material has been compacted to a required threshold. Additionally, since the determined stiffness value has the same engineering unit as a modulus of resilience, it allows for a broader range of applications, including, but not limited to, the use by design engineers for building and development (e.g. roads, buildings, etc.). As design guides may use a modulus of resilience as a primary input parameter when characterizing stiffness of work material, engineers may utilize this compaction method to ensure compliance with specification requirements.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

What is claimed is:
 1. A compactor, comprising: at least one roller drum configured to compact a work material; and a controller configured to: determine a propelling power of the compactor; access a calibration system including a reference propelling power value and correlation information between the reference propelling power value and a reference ground stiffness value; compare the propelling power of the compactor with the reference propelling power value; and determine a stiffness value of the work material based on a relationship between the propelling power of the compactor and the reference propelling power value; wherein the compactor is configured to adjust a compaction effort based on the determined stiffness value.
 2. The compactor of claim 1, wherein the controller is further configured to determine the stiffness value of the work material based on a difference between the propelling power of the compactor and the reference propelling power value.
 3. The compactor of claim 1, wherein the controller is further configured to use a regression method to determine the stiffness value of the work material.
 4. The compactor of claim 1, wherein the controller is further configured to send a signal to a display indicating whether the stiffness value of the work material meets a predetermined threshold.
 5. The compactor of claim 1, wherein the controller is further configured to determine the stiffness value of the work material as a physical characteristic parameter of the work material with a unit of force per area.
 6. The compactor of claim 1, wherein the controller is further configured to compare at least one of a type, a density, or a level of moisture content of the work material with reference material information in the calibration system, the reference propelling power value being determined in part based on this comparison.
 7. The compactor of claim 1, wherein the calibration system includes data obtained from a field measurement or a laboratory test.
 8. The compactor of claim 1, wherein the propelling power is determined based on at least one of a ground speed of the compactor, a rolling resistance of the compactor, or a compactive energy delivered by the compactor to the work material.
 9. A compactor, comprising: at least one roller drum configured to compact a work material; a memory storing a calibration system including a plurality of reference propelling power values, a plurality of reference ground stiffness values, and correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values; and a processor configured to: determine a propelling power of the compactor; compare the propelling power of the compactor with at least one of the plurality of reference propelling power values in the calibration system; and determine a stiffness value of the work material based on a relationship between the propelling power of the compactor and the at least one of the plurality of reference propelling power values.
 10. The compactor of claim 9, wherein the processor is further configured to determine the stiffness value of the work material based on a difference between the propelling power of the compactor and the at least one of the plurality of reference propelling power values.
 11. The compactor of claim 9, wherein the processor is further configured to use a regression method to determine the stiffness value of the work material.
 12. The compactor of claim 9, wherein the processor is further configured to send a signal to a display indicating whether the stiffness value of the work material meets a predetermined threshold.
 13. The compactor of claim 9, wherein the processor is further configured to determine the stiffness value of the work material as a physical characteristic parameter of the work material with a unit of force per area.
 14. The compactor of claim 9, wherein the processor is further configured to compare at least one of a type, a density, or a level of moisture content of the work material with reference material information in the calibration system, the at least one of the plurality of reference propelling power values being determined in part based on this comparison.
 15. The compactor of claim 9, wherein the calibration system includes data obtained from a field measurement or a laboratory test.
 16. A system for compacting at least one work material on a work site, comprising: a compactor having a variable compaction effort setting mechanism; a memory storing a calibration system including a plurality of reference propelling power values, a plurality of reference ground stiffness values, and correlation information between the plurality of reference propelling power values and the plurality of reference ground stiffness values; and a processor configured to: determine a propelling power of the compactor; compare the propelling power of the compactor with at least one of the plurality of reference propelling power values in the calibration system; determine a stiffness value of the at least one work material based on a relationship between the propelling power of the compactor and the at least one of the plurality of reference propelling power values; and produce a ground stiffness map for the work site based on the determined stiffness value and location information.
 17. The system of claim 16, wherein the processor is further configured to compare the determined stiffness value to a desired stiffness value.
 18. The system of claim 17, wherein the processor is further configured to command the compactor to adjust a compaction effort to achieve the desired stiffness value.
 19. The system of claim 18, further comprising a second compactor having a second variable compaction effort setting mechanism.
 20. The system of claim 19, wherein the processor is further configured to determine a second stiffness value from the second compactor and produce the ground stiffness map for the work site based on the stiffness value determined from the compactor and the second stiffness value determined from the second compactor.
 21. The system of claim 20, wherein the processor is further configured to command the compactor and the second compactor to achieve the desired stiffness value. 